Process and apparatus for air classification



Aug. 18, 1936. RKROURK; ,-051,1o7.

PROCESS AND APPARATUS FOR AIR CLASSIFICATION Filed Dec. 17, 1951'INVENTOR Rupert lfg fiourjae.

Patented Aug. 18, 1936 UNITED STATES PROCESS AND APPARATUS FOR AIRCLASSIFICATION Rupert K. Rourke, Lompoc, CaliL, asslgnor toJohns-Manville Corporation, New York, N. Y., a corporation of New YorkApplication December 17, 1931, Serial No. 581,639

6 Claims. (Cl. 209-145) This invention relates to a process andapparatus for the separation, by air classification, o! a relativelysmall coarse fraction from a finely divided powdered material, such ascomminuted diatomaceous earth or fullers earth. In this process thepowdered material is thoroughly dispersed in a rapidly moving air streamwhich is caused to change direction suddenly. The larger particles,because their mass is relatively large in proportion to theircross-sectional area, oiler greater resistance to change in direction ofmotion than does the main body of fine particles and are therebyseparated from the air stream containing the main body of fineparticles. A feature of this invention in its preferred embodiment is asecondary air stream which is caused to strike the primary air streamcontaining the suspended particles more or less at a right angle, at apoint near or preferably just beyond the point of deflection and in thatdirection toward which the primary stream is defiected. This secondaryair stream serves to wash out from the coarse particles a certain amountof desirable fines which would otherwise be included in the coarsefraction and thereby produces a sharper separation than could beobtained otherwise.

This invention relates particularly. to the removal of a smallproportion of grit and coarse agglomerates, such as would be retained ona 150 mesh screen, from a finely divided diatomaceous earth powder orthe like. A finely divided material of this nature ofiers unusualdifiiculties to classification by usual air separation methods, becauseof its extreme fineness, because all of the particles are of essentiallythe same density, and because of the fact that such particles show apronounced tendency to agglomerate to form larger particles. In thisinvention, effective dispersion of all the particles is maintainedbecause of the large volume of air and the high velocity at which it ismoving. Effective separation is secured by reason of the largedifierences in momentum of coarse and fine particles moving at this highvelocity and also because of the secondary transverse air stream whichwashes out from the coarse particles a large proportion of such fineparticles as have persisted undeflected in their direction of motion andwhich would otherwise be included in the coarse fraction. Thisseparation, furthermore, is accomplished without substantial injury tothe structure of the particles, which point is particularly important inthe case of diatomaceous earth filter aids, fillers, etc. in which theutility of the product depends to a large degree on preservation of thecharacteristic delicate diatomaceous structure.

An apparatus by which I may produce such a separation of flne fromcoarse material in milled diatomaceous earth, for example, is shown inFigs. 1, 2, and 3.

Fig. 1 represents a side elevation of the apparatus, Fig. 2 a verticalsection on line 22 of Fig. 3, and Fig. 3 a sectional plan view on line3-3 of Fig. 2. In the figures, like reference numbers indicate likeparts.

In Fig. 1, I indicates the intake, with adjustable damper la' throughwhich milled or partially milled mineral, as, for example, diatomaceousearth is fed to a high speed blower 2 or other means for producing anddelivering, at high speed, an aeriform suspension of a mineral powder,through the connecting pipe 3, within the narrow end of the truncatedcone 4. 5 is a closed cone disposed centrally within said truncated coneand defining therewith an annular opening between the circumferences oftheir bases. The inner cone 5 is supported by the rod 6 which fits, atthe lower end, adjustably into a seat or stufiing box I and, at theupper end, into the spider 8 provided with adjusting nut 8a. This innercone has its base at approximately the same level as or slightly higherthan that of the outer cone and has a more narrow base and flatter pitchthan the outer cone. 9 is a cylindrical hopper communicating with thesaid annular opening between the two cones and having an opening ill atits bottom which is closed by the gate ll. I2 is a funnel-shaped memberresting in a tee connection to the exhaust pipe l3 and held adjustablytherein by the set screws I 2a and l2b, which may be reached through thehandhole II with cover plate l8. The holes M are secondary or lateralair inlets or ports for admitting a lateral aeriform current adjacent tothe annular opening between the two cones. The size of these ports maybe adjusted by sliding the diaphragm I 4a upward or downward. I 5 is aninverted, relatively fiat cone closing the bottom of cone 5. I6 is anexhaust blower, which with its connections and adjustable damper lBa,provides exhausting means with entrance thereto disposed within thehopper 9 adjacent to the annular opening between the bases of the saidcones and adapted to defiect inwardly the aeriform stream issuingtherefrom, create a partial vacuum within the cyclone, and draw air inthru the lateral air ports It in the hopper 9. As stated, the funnelmember I2 is adjustable, upward or downward; it may be made to open justbelow the annular space between the two cones 4 and 5. The entrance tothe funnel or connection to the exhauster fan is suitably of diametersomewhat smaller than that of the said annular space between the twocones and is disposed below the said space. Also, the proportion ofprimary air coming in with the feed,

through pipe 3, and secondary air admitted laterally, through theopenings l4, may be varied by varying the size or speed oi the fans 2and IS, the number and size of the openings [4, the setting of one orboth of the dampers, and also the position of the inner cone withrespect to the outer cone, by moving the supporting rod 6 upward ordownward.

In the operation of the device, primary air car-- rying the particles tobe classified, passed through a blower 2 or other means to form anintimate suspension of the particles in the air. The resulting mixtureenters the conical member 4 through pipe 3, passes down through thespace between the outer cone 4 and the inner cone 5 and is there shapedinto an annular form moving in substantially non-sinuous manner and isthen drawn under the base of cone 5 into the funnelshaped member II, byinward suction produced by the exhauster fan l6 connected to the pipel3. This causes sharp deflection of the stream of annular cross sectiontowards the direction of radii of the said cross section, as, forexample, towards the inside of the annular band, as illustrated. Thisdeflection is flatwise of the band, that is, in the direction (towardsthe direction) of the shortest dimension of the stream in any localizedarea. Secondary air is drawn in through the lateral openings l4,suitably at almost a right angle to the original direction of theprimary air stream, and passed also into the funnel l2. Coarse particlescontinue downward, outside the funnel member l2, and are caught inhopper 9, while the aeriform stream and flne particles are deflected, asfor example, inwardly at an angle of less than 90 from the direction inwhich the stream issues from the annular opening, into the funnel memberI! and thence through pipe l3 and the fan [6 to a suitable cyclonic dustcollector (not shown).

The apparatus is suitably arranged so that the cones 4 and 5 (Fig. 1)are in an upright position. In such a case the narrow end or thetruncated cone becomes the upper end.

For continuous operation gate l may be replaced by a rotary seal.

As stated, I have found this invention useful in classifying comminutedor milled mineral substances. Thus, I have classified satisfactorily adiatomaceous earth that was calcined subsequent to being milled to adegree of fineness approximating that of the filter-aid known as Filter-Cel. I have also classified a diatomaceous product consisting ofcalcined milled diatomaceous earth and corresponding closely to thecommercial product known as Hyflo Super-Gel, particularly the HyfloSuper-Gel" as first made and containing a certain percentage ofrelatively coarse glassy aggregates or of soft lumps. The invention hasbeen found especially useful in separating particles too large to passthrough a 150- mesh screen from those that are finer.

The thoroughness of separation of fines from coarse may be controlled bychanging (a) the proportion of secondary and primary air, as describedabove, (12) the width of the annular opening between cones 4 and 5, (c)the width of opening between the cone and the funnel member l2, (d) theposition of the latter member with respect to that of the air ports l4,(e) the speed of movement of the aeriform suspension, and (f) theproportion of dust in-the said suspension. In general, thoroughness ofseparation of coarse particles from the fines in the primary aeriformstream is favored, for example, by a high pro-, portion of primary tosecondary air, narrow openings only between the bases of cones 4 and 5and between the base of the inner cone and the top of the funnel member,and a high speed oi movement of the aeriform suspension. The proportionof flnes going with coarse material, on the other hand, is decreased bythoroughly washing the separated stream of coarse particles with thelateral air stream.

The following details or construction and operation illustratea'speciflc example of the practice of my invention. Into an outertruncated cone, of vertical height 90 inches and of diameter 18 inchesat the top and 54 inches at the bottom, there is blown a suspension or100 pounds calcined milled diatomaceous earth in 9,400 cu. ft. air perminute. Adjustments of the apparatus are so made that there is 1.52 sq.ft. of area of the annular opening between the inner and outer cones 4and 5, at the closest point, and 1.76 sq. ft. of area of the annularopening between the tunnel member I! and the base of the inner cone,also at the closest point. Lateral or secondary air is admitted at therate of 4,100 cu. ft. per minute.

From the preceding data, it may be calculated that the thickness of theband of primary aeriform suspension issuing from the annular openingbetween the outer and inner cones is less than 3 inches or about 1.4inches and the linear speed approximately 103 ft. per second. The mixedprimary and lateral air streams pass the most narrow part of the openinginto the funnel member l2 at a linear speed somewhat higher than 103ft.per second.

The coarse fraction was collected in the hopper 9, the flnes or majorfraction in a cyclonic dust separator. Analysis of the flnes showed apercentage of particles that failed to pass through a 150-mesh screen ina wet screening test that was approximately only half of the percentageof such coarse particles contained in the material before passingthrough the air classifier.

In other typical operations with the same 4112- paratus the amount ofthe primary aeriform suspension blown in per minute has varied from6,200 to 8,500 cu. ft. per minute; the linear speed through the annularopening between cones 4 and 5, from 64 to 93 feet per second; thecontent of suspended diatomaceous earth from 85 to 110 pounds; thelateral or secondary air stream from 2,400 to 7,600 cu. ft., the area ofannular opening between the inner and outer cones, at the closest point,from 0.83 to 1.68 sq. ft., and the area of opening between the base ofthe inner cone and the funnel member, also at the closest point, from1.34 to 1.68 sq. ft. The percentage oi material flner than 150 mesh thatis collected with the coarse, in hopper 9, varies from 13 to 95 per centof the total weight of the coarse fraction. When the lateral orsecondary air stream is used in amount in excess of 5,250 cu. it. aminute, the separated coarse fraction contains only 13 to 28 percent oflines, thus showing the effectiveness of treating the separated coarsefraction with an adequate lateral air stream or blast, to wash out theflnes.

The above description of apparatus and process are given by way ofillustration, not limitation, of the invention. Many changes in theapparatus illustrated may be made without departing from the spirit ofthe invention. Thus the pitch of the conical members 4 and 5 may bevaried or they may be substituted by other members of circular crosssection, as, for example, by inner and outer concentric pipes, the innerpipe being closed at the upper end and suitably also at the lower. Or, arectangular slot that is relatively long in pro portion to its width maybe used and the thin stream or band of air-dust suspension passedthrough it in substantially unidirectional manner and then deflectedfiatwise, suitably with a lateral blast of air impinging on it adjacentto the point of deflection and in the general direction towards whichthe band is deflected. However, I have found the use of cones verydesirable in distributing the air-dust stream and in making it into anannular form or band, moving at a high speed in a course that issubstantially unidirectional, with a minimum of eddies or crosscurrents. Difierent means of collecting the classified particles may beused.

In separating particles by this invention, the particles to beclassified should enter the classifier proper at high velocity and witha very large weight of air in proportion to the suspended solid, tominimize aggregation of individual particles into clusters. Instead ofan air suspension there may be used an aeriform suspension, as, forexample, a suspension of particles of solid in an aeriform stream suchas one of flue gas,

The terms substantially non-sinuous" and unidirectional, as applied tothe manner of movement of the shaped stream of gas, are intended toindicate a degree of freedom from turbulence that is not realized whenthe stream of gas is being subjected continuously to change ofdirection, as in a spirally shaped pipe. An intimate suspension is onein which the particles to be classified are separately suspended, innonaggregated form. In the preferred embodiment of the invention, theshape of the gas stream at the point of deflection is annular, that is,the shape of a ring of little thickness or shortest dimension,corresponding to the distance between the circumference of the bases ofthe cones 4 and 5. After the classification of the original suspensionby sharp deflection is completed and the separated coarse particles arewashed by the secondary air stream, the secondary air used in washing isblended, as in the member l2, with the portion of the originalsuspension remaining subsequent to sits sharp deflection; in this mannerfines in the primary and secondary air streams are composited.

The term band, as used herein, means a shaped mass of material ofrelatively great length and little thickness at a given point.

The details that have been given are for the purpose of illustration,not restriction. It is intended that variations within the spirit of theinvention should be included within the scope of the claims.

What I claim is:

1. A classifier of the character described comprising a hollow truncatedcone, a closed cone disposed centrally within said truncated cone anddefining therewith an annular opening between the circumferences oftheir bases, a hopper communicating with the annular opening, means ofdelivering, at high speed, an aeriform suspension of a mineral powderwithin the narrow end of the truncated cone, air exhausting meansdisposed adjacent said annular opening adapted to deflect the aeriformstream issuing therefrom, and means for admitting a lateral aeriformcurrent into the first mentioned aeriform stream adjacent the zone ofdeflection.

2. A classifier of the character described comprising a hollow truncatedcone, a closed cone disposed centrally within said truncated cone anddefining therewith an annular opening between the circumferences oftheir bases, a hopper communicating with the annular opening, means ofdelivering, at high speed, an aeriform suspension of a mineral powderwithin the narrow end of the truncated cone, and air exhausting meansdisposed adjacent said annular opening adapted to deflect the aeriformstream issuing therefrom, whereby a separation of the coarse particlesfrom the aeriform stream is effected.

3. In a classifier of the type described, means for forming an intimatesuspension in a gas of finely divided solid material containing fine andrelatively coarse particles, means for shaping the suspension into anannular form moving rapidly in substantially unidirectional manner,means for deflecting sharply the gas content of the suspension in thesaid annular form, whereby separation of the relatively coarse particlesfrom the fine particles is effected, means for washing the separatedcoarse particles with a secondary gas stream, and means for blending thesecondary gas used in the washing with the portion of the originalsuspension remaining subsequent to the sharp deflection of the saidoriginal suspension.

4. In classifying particles of various sizes of finely divideddiatomaceous earth, the method which comprises forming the saidparticles into a dilute suspension in an aeriform stream, forming thesuspension into a thin band moving at a linear speed in excess ofsixty-four feet per second, and sharply deflecting the band towards thedirection of the shortest dimension thereof at any given localizedportion, whereby separation of the particles of various sizes iseffected.

.5. In classifying particles of various sizes of finely divideddiatomaceous earth, the method which comprises forming the saidparticles into a dilute suspension in an aeriform stream, includingaeriform material in proportion of the order of at least 6,400 cubicfeet for each 110 pounds of diatomaceous earth, forming the said streaminto a thin band of high speed, and sharply deflecting the band fiatwisewhile maintaining high speed thereof.

6. A classifier of the character described comprising an upright hollowmember of circular cross section, a smaller upright hollow element ofcircular cross section, disposed within the said member and terminatingat its lower end approximately at the same level as the lower end of themember and defining an annular opening therewith, means for delivering,through the said opening, an aeriform suspension of the material to beclassified, moving at high speed in substantially unidirectional manner,an exhauster fan and connections thereto including a circular entrancemember disposed adjacent to and below the said annular opening and beingof diameter smaller than that of the said opening, a hopper memberdisposed around and generally below the said opening and communicatingtherewith, and air ports in the hopper for admitting secondary airlaterally to the said annular opening, the said exhauster fan beingadapted to draw the said suspension in the form of a band through thesaid opening, to cause sharp deflection of the band into the saidcircular entrance member, and to draw auxiliary air through the saidports and through the separated coarse particles and then blend theauxiliary air with the deflected stream.

RUPERT K. BOURKE.

